Specifications for materials used in pharmaceutical and cosmetic compositions must meet rigid specifications (official monographs) described, for example, in the U.S. Pharmacopeia XX and National Formulary XV. Magnesium Aluminum Silicate, sold by R. T. Vanderbilt Co. in the pharmaceutical and cosmetic industry, i.e. for use in anti-dandruff shampoo, has very rigid and narrow monographs, apparently derived from a rare clay, mined by R. T. Vanderbilt from a location miles under ground level. A combination of the rare clay with other clays meets the official monograph for magnesium aluminum silicate since the rare clay does not contain any significant amount of contamination, such as calcite (calcium carbonate) or dolomite (calcium manesium carbonate).
The official monograph for Magnesium Aluminum Silicate is written very narrowly for pH, viscosity, Aluminum/Magnesium ratio and acid demand so that prior to the present invention, it has been impossible to meet the official monograph without including at least a portion of the R. T. Vanderbilt rare, uncontaminated clay in the Magnesium Aluminum Silicate composition.
The official monograph for Magnesium Aluminum Silicate defines the material as "a colloidal montmorillonoid saponite, in which magnesium has substantially replaced aluminum in the crystal lattice, that has been processed to remove grit and non-wettable ore components."
Previous attempts by this assignee to wash and otherwise process contaminated clays in an attempt to meet the official monograph for Magnesium Aluminum Silicate have been unsuccessful. Consequently, prior to the present invention, R. T. Vanderbilt Co. has been the only supplier of Magnesium Aluminum Silicate to the pharmaceutical and cosmetics industries.
The specification for Al/Mg ratio is achieved by blending together a dioctahedral montmorillonite clay with saponite, sepiolite, talc and/or hectorite (trioctrahedral clay). Saponite, sepiolite, talc and hectorite each include very little or no aluminum and a significant amount of magnesium in the form of magnesium oxide; and dioctahedral montmorillonites, such as bentonite, have little or no magnesium and a significant amount of aluminum in the form of aluminum oxide. Any required Al/Mg ratio can be achieved by blending the montmorillonite with saponite and/or hectorite. However, the specifications for Magnesium Aluminum Silicate call for very specific viscosity and acid demand requirements as follows:
Viscosity--After determining the Loss on drying, weigh a quantity of Magnesium Aluminum Silicate test specimen equivalent to 25.0 g on the dried basis. Over a period of a few seconds, transfer the undried test specimen to a suitable 1-liter blender jar containing an amount of water, maintained at a temperature of 25.degree..+-.2.degree. C., that is sufficient to produce a mixture weighing 500 g. Blend for 3 minutes, accurately timed, at 14,000 to 15,000 rpm (high speed). (Note-Heat generated during blending causes a temperature rise to above 30.degree..) Transfer the contents of the blender to a 600-ml beaker, allow to stand for 5 minutes and adjust, if necessary, to a temperature of 33.degree..+-.3.degree.. Using a suitable rotational viscometer, operate the viscometer for 6 minutes, accurately timed, and record the scale reading. Convert the scale reading to centipoises by multiplying the reading by the constant for the viscometer spindle and speed employed.
______________________________________ Al content/ Viscosity (cps) Mg content Type Min. Max. Min. Max. ______________________________________ 1A 225 600 0.5 1.2 1B 150 450 0.5 1.2 1C 800 2200 0.5 1.2 11A 100 300 1.4 2.8 111A 250 500 3.5 5.5 111B 40 200 3.5 5.5 ______________________________________
Acid demand--After determining the loss on drying, weigh a quantity of Magnesium Aluminum Silicate equivalent to 5.00 g, and disperse in 500 ml of water with the aid of a suitable blender fitted with a 1-liter jar. Using a stopwatch, designate zero time. With consant mixing, add 3.0-ml portions of 0.100 N hydrochloric acid at 5, 65, 125, 185, 245, 305, 365, 425, 485, 545, 605, 665, and 725 seconds, and add a 1.0-ml portion at 785 seconds. Determine the pH potentiometrically at 840 seconds: the pH is not more than 4.0.
The lower the Al/Mg ratio required for a particular type of Magnesium Aluminum Silicate, the more hectorite and/or saponite required. Too much hectorite increases viscosity beyond specifications and too much saponite causes stability problems, as determined by any separation of a slurry of the material in water upon standing about 24 hours. If all three clays do not contain any significant contamination, it is possible to blend the montmorillonite and hectorite or montmorillonite and saponite or all three types of clay to achieve the desired specifications. If any of the clays contain non-clay minerals such as calcite (calcium carbonate) or dolomite (calcium magnesium carbonate), however, the clay composition will probably fall out of specification for acid demand. At a pH below about 6, the carbonate will convert to carbon dioxide, generating gas and the pH will buffer back above the pH 4 acid demand specification.
Acid demand is an extremely difficult requirement to meet while maintaining the required Al/Mg ratio. In accordance with the specifications, after incremental additions of 40 ml. of 0.1 N HCl, the pH of the material must be 4.0 or less. Almost all available hectorite and saponite contain sufficient contamination to fall out of specification for acid demand when combined with commonly available montmorillonite. The hectorite is contaminated with calcite and the saponite is contaminated with dolomite. Also, the montmorillonite, as mined, generally has little or no sodium so it becomes necessary to add sodium carbonate to convert the clay from its non-colloidal state to a colloidal clay. The added carbonate in the treated montmorillonite contributes to the acid demand problem.
Attempts to form a blend of 70% montmorillonite, 20% hectorite and 10% saponite to achieve an Al/Mg. ratio of 1.0 results in a Magnesium Aluminum silicate which does not meet the acid demand specification. Five grams of the product includes 0.7(5)=3.5 grams of montmorillonite; 0.2(5)=1.0 gram of hectorite; and 0.1(5)=0.5 gram of saponite per 500 milliliters of water. The montmorillonite required 27 milliliters of 0.1 N HCl to reduce the pH to 4.0; the hectorite required 13 milliliters to reduce the pH to 4.0; and the saponite required 3 milliliters for a total of 43 milliliters. The specification calls for a pH of 4.0 or less upon the addition of 40 milliliters of 0.1 N HCl.
One might suspect acid demand could be met if the blend ratios were changed. For example, since the saponite only requires 3 milliliters of acid to lower the pH to 4.0, conceivably one could add more saponite and less hectorite to meet acid demand. However, since the saponite is acid treated, by increasing the amount of saponite, the final product would fall out of specification for pH, which is 9-10. Also, due to the excess acid in the saponite, an acid stability problem would result. Further, lowering the amount of sodium carbonate treatment of the montmorillonite would lower the acid demand within specifications, but then the added sodium would be insufficient to convert the clay to a colloidal state and, therefore, the product would not meet viscosity specifications.
The product needs hectorite and/or saponite to meet the aluminum/magnesium ratio. If the product contains all hectorite, however, the viscosity would be out of specification because hectorite has a very high viscosity. Hectorite also contributes to the acid demand problem. Saponite, can be blended with hectorite to meet the Al/Mg ratios, but too much saponite causes the pH to be out of specification and creates acid stability problems. Sodium carbonate treatment is needed for the contaminated montmorillonite, even if thoroughly washed, to achieve a colloidal clay. The carbonate treatment of the montmorillonite contributes to an acid demand problem and also increases the pH so that the final product could fall out of specification for pH. Because of all these problems, specifications for Magnesium Aluminum Silicate have been very difficult, if not impossible, to meet.
Further, in many cosmetic and pharmaceutical suspensions, i.e. antiperspirant compositions, it is necessary for the purpose of stability or other reasons that the suspension have a relatively low pH in the range of about 2.0 to about 5.0. Bentonite clay alone slurried in water will yield a bentonite suspension having an alkaline pH, normally with the range of about 8.5 to about 11.0 or 12.0 using quantities of bentonite typical in the manufacture of cosmetic and pharmaceutical suspensions. The addition of one or more acids, for example hydrochloric or phosphoric acid to a bentonite clay slurry to achieve a pH in the range of about 2.0 to about 5.0, or 5.5, and generally below about 6.0, has caused typical bentonite suspensions to lose its suspending capacity, resulting in flocculation and settling of the bentonite from the suspension. Accordingly, prior to the present invention, only very pure grades of bentonite, i.e. white bentonite, having very few impurities could be used in a water suspension having a pH below about 6.0 without the formation of precipitates.
Prior to the present invention, bentonite clays have been modified by ion exchange resins to increase the sodium content or to exchange one polyvalent cation for another on the clay, but prior to the present invention no one has enriched bentonite with hydrogen by contact with a hydrogen ion exchange resin for the purpose of manufacturing a hydrogen enriched clay having reduced acid demand and capable of excellent stability in a water containing suspension having a pH below about 6.0, i.e., 2.0 to 5.5. The following patents disclose ion exchange of clays to provide a sodium enriched clay, or to exchange one polyvalent ion for another on the clay structure: U.S. Pat. Nos. 2,404,038 to Cardwell; 3,158,579 to Pollitzer et al.; 3,993,500; 4,028,133; and 4,047,738 to Issac et al. and U.S. Pat. No. 4,271,043 to Vaughan et al.